Explain by giving two examples why the measurement of a physical quantity is expressed as a combination of a numeral and a unit.

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Solution

To measure a physical quantity, we need to compare it with a known fixed physical quantity of the same kind, i.e., a unit. Hence, the measurement of a physical quantity is always written as a combination of a numeral along with the unit. The numeral specifies the number of times the unit is repeated. Example:
1. Using a centimetre scale, the length of pencil box is found to be $20$ centimetres (cm). $20 c m$ simply means that the length is $20$ times a centimetre. (The centimetre forms the unit of length in a centimetre scale). Here, the number $20$ is the numeral (magnitude) and cm is the unit.
2. Using a weighing (kilogram) scale, the weight of the box is found to be $2$ kilograms (kg) $2$ kg simply means that the mass of the box is $2$ times a kilogram. (The kilogram forms the unit of mass in a kilogram scale). Here, the number $2$ is the numeral (magnitude) and kg is the unit.

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